Display screen or portion thereof with a graphical user interface



FIG. 1 is a face view of a display screen or portion thereof with a graphical user interface, showing my new design and illustrating a first embodiment of the design; and,

FIG. 2 is a face view of a display screen or portion thereof with a graphical user interface, illustrating a second embodiment of the design.

The broken line showing of the display screen and the remainder of the graphical user interface are included for the purpose of illustrating environmental structure, and the broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 